The present invention relates to a portable radio communication device.
Portable radio communication devices, in particular mobile phones, are becoming increasingly commonplace nowadays. Accordingly, the design of a mobile phone must take into consideration factors such as the different environments in which the mobile phone is likely to be used. In particular, given that mobile phones are typically used on-the-move and out-of-doors, it is important that they be resistant to the ingress water. Preferably, mobile phones should be rain proof, or at least shower proof.
Mobile phones are also increasingly being carried around and used during sports activities so that the user is ever contactable. For example, it is not uncommon for a user to take a mobile phone along with him/her whilst jogging. This places a new set of demands in the design of a mobile phone. Whilst of course, the mobile phone must be small and lightweight, it must also be solid, robust and capable of withstanding rain and sweat.
In currently available mobile phones, the risk of water ingress is conventionally tackled by providing fluid tight seals, gaskets and plugs in areas where the phone is susceptible to water getting in, e.g. at external connections such as the system connector. Current mobile phone designs however do not provide entirely satisfactory protection against water ingress. Furthermore, current phones not able to deal with the demands placed on them by sports usage.
Accordingly, the present invention provides a portable radiotelephone device comprising a body having provided on one or more exposed surface thereof one or more electrical contact means for one or more respective electrical input/output means, wherein said one or more electrical contact means is covered with one or more layers of electro-resistive material, said electro-resistive material in the relaxed condition being an electrical insulator and in the stressed state being an electrical conductor, the arrangement being such that to effect electrical connection between any of the one or more electrical contact means with respective one or more electrical input/output means, respective contact means and input/output means are mutually engaged so as to load the elasto-resistive material under compression.
By means of the invention, the exposed electrical contact points of the mobile phone on external surfaces thereof are sealed against the ingress of water, in a compression contacting system. More specifically, the elasto-resistive (ER) material with its polymer composition provides a seal at the phone""s external electrical contact points. This represents a considerable improvement over the prior art radiotelephones in which the electrical contacts are traditionally constructed from copper are vulnerable to water ingress and to corrosion. Furthermore, the ER material affords increased wear and in general provides for an altogether more robust phone
The basic operating principle of the ER material is that its resistance reduces as a mechanical force is applied, changing from being an insulator to a conductor when mechanically loaded. The applied loading may be compression, tension, torsion or shear forces. The chemical composition and structure of an ER material basically comprises an elastically deformable polymer that includes an electrically conductive filler spread out within and encapsulated by, the non-conductive elastomer structure, and a modifier which promotes the elasticity of the material. Accordingly, the ER material exhibits a change in its bulk conductivity from that of the elastomer to that of the entrapped conductive filler particles. Further details of a suitable ER material are given in patent publication PCT/GB98/00206. The properties of the elasto-resistive material described in this PCT publication are as follows: in an unstressed state the elasto-resistive material is an insulator with resistance of between 1012 to 1014 ohms per centimeters. Upon loading the resistance decreases to between 1 to 100 micro ohms per centimeter. It has been found that resistance is inversely proportional to the load applied. Furthermore, by varying the chemical composition of the material, the force needed to change state can be adjusted from being a heavy point load at the high end, down to audio sensitivity at the lower end, e.g. speech activation.
The elasto-resistive material may be a polymer composition comprising electrically conducting particles encapsulated within an electrically insulating elastomer, the ratio of the conducting particles to the non-conducting elastomer being such that the electrical resistivity of the material varies in a linear manner in response to the application of force to the material.
The conductive filler may be a metal powder such as Ni INCO 287. The elastomer may be a silicone elastomer based on polydimethylsiloxane and having a low surface energy, and being high on the triboelectric series. The modifier may be fumed silica.
Conveniently, the ratio of conductive filler to elastomer is in the range 1:1 to 3:1.
Advantageously, the use of the ER material provides for localised conduction between respective electrical connections.